The present invention relates to an oxide superconductor which can be used for superconducting cables, superconducting magnets, current lead wires, and the like, a manufacturing method therefor, and a base substrate therefor. Specifically, the present invention relates to a technique in which an oxide superconductor layer is formed on an intermediate layer on a substrate using a liquid phase epitaxial method.
A superconductor oxide has an electric anisotropy such that an electrical current flows easily in a fixed direction and hardly flows in another fixed direction with respect to a crystallographic axis thereof. When an oxide superconductor is prepared using superconductor oxides, since the superconductor oxides have such electric anisotropy, a problem arises in that it is necessary to orientate crystals of the superconductor oxides in the fixed direction in which an electrical current flows.
In addition, since the superconductor oxide is one of ceramic, it has a low tolerance to bending or distortion. Therefore, in order to use the superconductor oxides for superconductors, such as superconductor wire, a thin film oxide superconductor layer is formed on a metallic substrate, such as a flexible tape.
In light of the above, as one example of means for forming the oxide superconductor layer on the metallic tape substrate, a vapor phase method, such as a laser evaporation method and a chemical vapor deposition (CVD) method, has been used.
In such a vapor phase method, an oxide superconductor layer having an excellent crystalline orientation can be prepared. However, for the vapor phase method, it is necessary to gradually deposit superconductor oxide crystals in a film manufacturing room, such as a chamber in a reduced pressure atmosphere, while the crystalline orientation of the superconductor oxide is observed. Therefore, the film formation rate is extremely low. For example, the film formation rate of the CVD method, which is believed to have a relatively high film formation rate is only about 0.01 xcexcm/min. Therefore, it is difficult to stably prepare an oxide superconductor having a long length. If an oxide superconductor having a long length can be prepared, the required time for preparing is too long.
In addition, in view of a practical use of an oxide superconductor as a conductor, it is necessary to carry a high current; however, the oxide superconductor layer which is obtained by the vapor phase method has a thin film shape. In the vapor phase method, it is difficult to prepare an oxide superconductor layer having a sufficient thickness. Therefore, the vapor phase method has a problem in that it is difficult to prepare an oxide superconductor layer which can resist a high voltage.
Consequently, in the well-known vapor phase method, it is difficult to increase the thickness of the oxide superconductor layer and to carry a high current, and difficult to prepare the oxide superconductor layer at a high speed and to realize a high productivity.
Recently, a liquid phase epitaxial method has been suggested as a method which can prepare a thick film oxide superconductor layer at a high film formation rate.
The liquid phase epitaxial method is a method in which a solution having a similar composition to that of the objective superconductor oxide is used, a substrate is put into the solution, and is then gradually pulled up from the solution, and thereby an oxide superconductor layer is formed at the surface of the substrate where it is pulled up from the solution. In the liquid phase epitaxial method, a thick film oxide superconductor layer, of which the thickness is several tens of times as large as the thickness of the oxide superconductor layer prepared by a vapor phase method, can be prepared at a high film formation rate.
However, when a substrate in a tape shape is put into a solution in order to prepare an oxide superconductor layer on the substrate by the vapor phase epitaxial method, and the substrate is made of high heat resistant metals, but the metallic substrate reacts easily with components contained in the solution, there is a possibility that the substrate will dissolve into the solution. In addition, since the superconductor oxide is required to have an excellent crystalline orientation, when the components of the substrate dissolve into the solution, there is a possibility that elements which are not desired may contaminate the superconductor oxide. Due to this, there is a possibility that the crystalline structure of the superconductor oxide will remarkably deteriorate.
In consideration of the above, an object of the present invention is to provide an oxide superconductor comprising a thick film oxide superconductor layer on a substrate. In addition, another object of the present invention is to provide an oxide superconductor in which a substrate and a solution do not react when an oxide superconductor layer is prepared by the liquid phase epitaxial method, and which comprises a thick film oxide superconductor layer having an excellent crystalline orientation; and to provide a base substrate which is suitably used for preparing the oxide superconductor.
The present invention has an object of providing a manufacturing method for an oxide superconductor which can prepare a thick film oxide superconductor layer on a substrate at a film formation rate which is remarkably higher than that of an oxide superconductor layer formed by a vapor phase method. In addition, the present invention has another object of providing a manufacturing method for an oxide superconductor, in which when a substrate provided with an oxide intermediate layer is put into a solution and a raw oxide superconductor layer is prepared by a liquid phase epitaxial method, the raw oxide superconductor layer is prepared without damage to a substrate due to a solution.
In consideration of the above, the present invention has another object of providing an oxide superconductor which comprises a thick film oxide superconductor layer on a substrate and which has a high critical current.
In order to solve the above-mentioned problems, the present invention provides an oxide superconductor comprising: a substrate made of metals having a high melting temperature; at least one oxide intermediate layer which is formed on at least one surface of the substrate; and a thick film oxide superconductor layer which is formed on the oxide intermediate layer by the liquid phase epitaxial method in which the substrate provided with the oxide intermediate layer is put into a solution containing the elements comprising an oxide superconductor layer, and is then pulled out from the solution.
In the oxide superconductor, it is preferable for the oxide intermediate layer to comprise a first intermediate layer formed at the substrate side and a second intermediate layer formed at the oxide superconductor layer side; the first intermediate layer to be made of materials having a low reactivity to the substrate and the second intermediate layer; the second intermediate layer to be made of materials having a low reactivity to the first intermediate layer and the solution; and the thick film oxide superconductor layer to be prepared by being grown by the liquid phase epitaxial method from a seed layer for the superconductor oxides which is formed on the second intermediate layer.
In the oxide superconductor, it is also preferable for the substrate to be made of an Ni alloy or a Zr alloy; the first intermediate layer to be made of oxides containing a metal selected from the group consisting of Ni, Mg, Ba, and Zr; and the second intermediate layer to be made of oxides containing Ba.
In addition, it is preferable for the oxide superconductor to comprise a substrate which is made of an Ni alloy having a high melting temperature; a first intermediate layer which is made of MgO and is formed on the substrate; a second intermediate layer which is made of BaZrO3 and is formed on the first intermediate layer; and an oxide superconductor layer which has a composition represented by the general formula RE1+XBa2xe2x88x92XCu3Oy wherein RE denotes at least one element selected from the group consisting of Y, Nd, Sm, Eu, Er, Dy, Gd, Ho, Tm, and Yb.
The present invention provides a base substrate for an oxide superconductor comprising: a substrate which is made of metals having a high melting temperature; a first intermediate layer which is formed on the substrate; and a second intermediate layer which is formed on the first intermediate layer, wherein the substrate is made of metals having a high melting temperature; the first intermediate layer is made of oxides which have a low reactivity to the elements comprising the substrate and the second intermnediate layer, and the second intermediate layer is made of oxides which have a low reactivity to the elements comprising the first intermediate layer, a heat resistance which is higher than that of the first intermediate layer, and a low reactivity to a solution for the superconductor oxides.
The present invention provides a manufacturing method for an oxide superconductor comprising the steps of: forming at least one oxide intermediate layer and a seed layer for the superconductor oxides on at least one surface of a substrate made of metals having a high melting temperature; carrying out the liquid phase epitaxial method in which the substrate provided with the oxide intermediate layer and the seed layer is put into a solution containing the elements comprising the oxide superconductor layer and is then pulled up from the solution, and thereby the seed layer grows on the oxide intermediate layer, and a raw oxide superconductor layer is formed; and heat treating the raw oxide superconductor layer, and thereby the raw oxide superconductor layer is converted into an oxide superconductor layer.
In the manufacturing method, it is preferable for the oxide intermediate layer to comprise a first intermediate layer which is formed on a substrate side and a second intermediate layer which is formed on a raw oxide superconductor layer side; the first intermediate layer to be made of materials which have a low reactivity to the substrate and the second intermediate layer; and the second intermediate layer to be made of materials which have a low reactivity to the solution.
In the manufacturing method, it is also preferable for the substrate to be made of an Ni alloy or a Zr alloy, the first intermediate layer to be made of oxides containing a metal selected from the group consisting of Ni, Mg, Ba, and Zr, and the second intermediate layer to be made of oxides containing Ba.
In addition, in the manufacturing method, it is preferable for the substrate to be made of an Ni alloy which has a high melting temperature; the first intermediate layer to be made of MgO; the second intermediate layer to be made of BaZrO3; and the oxide superconductor layer to have a composition represented by the general formula REBaCuO, wherein RE denotes at least one element selected from the group consisting of Y, Nd, Sm, Eu, Er, Dy, Gd, Ho, Tm, and Yb.
In order to achieve the above-mentioned objects, the present invention provides another oxide superconductor comprising: a substrate which is made of metals having a high melting temperature; a main oxide intermediate layer which is formed on at least one surface of the substrate; a seed layer for the superconductor oxides which is formed on the main oxide intermediate layer; an oxide superconductor base layer which contains at least one element contained in the main oxide intermediate layer and is formed on the seed layer for the superconductor oxides by a liquid phase epitaxial method; and a thick film oxide superconductor layer which is formed on the oxide superconductor base layer by a liquid phase epitaxial method.
In the oxide superconductor, it is preferable for the main oxide intermediate layer to be made of MgO or NiO; and the oxide superconductor base layer which contains the elements comprising the main oxide intermediate layer to contain MgO or NiO.
In the oxide superconductor, it is preferable for the substrate to be made of an Ni alloy or a Zr alloy; and the main oxide intermediate layer to be made of oxides containing a metal selected from the group consisting of Ni, Mg, Ba, and Zr.
It is also preferable for the oxide superconductor layer to have a composition represented by the general formula REBaCuO, wherein RE denotes at least one element selected from the group consisting of Y, Nd, Sm, Eu, Er, Dy, Gd, Ho, Tm, and Yb.
The present invention provides another manufacturing method for an oxide superconductor comprising the steps of: forming a main oxide intermediate layer and a seed layer for the superconductor oxides on at least one surface of a substrate which is made of metals having a high melting temperature; carrying out the liquid phase epitaxial method in which the substrate provided with the main oxide intermediate layer and the seed layer is put into a solution containing the elements comprising both the superconductor oxides and the main oxide intermediate layer and is then pulled up from the solution and thereby a thin film oxide superconductor base layer is formed on the seed layer; carrying out the liquid phase epitaxial method in which the whole of the product prepared in these steps is put into a solution containing the elements comprising superconductor oxides and is then pulled up from the solution, and thereby a thick film raw oxide superconductor layer is formed on the oxide superconductor base layer; and heat treating the raw oxide superconductor layer and thereby the raw oxide superconductor layer is converted into a thick film oxide superconductor layer.
In the manufacturing method, it is preferable for the substrate to be made of an Ni alloy or a Zr alloy; and the main oxide intermediate layer to be made of oxides containing a metal selected from the group consisting of Ni, Mg, Ba, and Zr.
In addition, it is also preferable for the solution containing the elements comprising superconductor oxides and the main oxide intermediate layer to be prepared by adding the elements comprising the main oxide intermediate layer in a solution containing the elements comprising the superconductor oxides so as to reach saturation.